Aphids and Scale Insects

Whitney CranshawColorado State University

Western Colorado Pest

Management Workshop

AphidsHemiptera: Aphididae

Aphids can range in size,

shape and patterning

Aphids associated

with Prunus spp.

Aphids associated with Acer spp.

Rose Aphids

Aphids associated with

willow (Salix spp.)

Largest Aphid in RM Region – Giant Willow Aphid

Giant conifer aphids Cinara species

Different species are

present on junipers,

spruce and pines

Some aphids are covered with finely powdered wax

Some aphids – known as “woolly aphids” – have wax

that form long filaments and may cover their body

Woolly Apple Aphid

Leafcurl Ash Aphid

Sugarbeet root aphid

Rice root aphid Aphids on dandelion roots

Some aphids

are associated

with roots of

plants

Root-infesting

aphids are often

surrounded by

wax

Aphid life cycles – All

aphids go through three

feeding stages, each

punctuated with a

molting event

Aphids will molt 3 or 4

times in their life,

becoming an adult after

the last molt

Diagnostic: Cast skins remain after aphids molt

Aphids on stem (left)

and cast skins

dropped onto leaf

(right)

Toothache plant infested

with green peach aphid

Asexual reproduction – giving live birth to a genetically

identical daughter – is the norm for aphid reproduction

Aphid

populations

can increase

rapidly

Live birth and asexual

reproduction are the

norm with aphids

Adults may be winged

or wingless

Developing wing pads

on aphid nymph

Adults may be winged

or wingless

How do aphids survive

winter in areas with

freezing temperatures?

• Outdoors

–Eggs that remain dormant through winter• Survives on perennial host or crop debris

– Nymphs, adults in continuous reproduction

• Rare and requires living hosts through winter

• Indoors

– Nymphs, adults in continuous reproduction

Outdoors, almost all

aphids have a holocyclic

life cycle and produce

eggs in autumn. That is

normally the stage that

survives between

seasons.

Overwintered eggs of rose aphid Rose aphids on flower buds

Egg producing form

female mating with

winged male Winged male

Egg producing form

female with recently

laid eggs

Sexual forms of cannabis aphid and eggs

Late September on a hemp leaf

Most aphids lay the overwintering eggs on a

perennial (often woody) plant

Holocyclic

Life Cycle –

with host

alternation

Life cycle involves a

winter host plant and

a different summer

host plant(s)

Green Peach AphidMyzus persicae

An example of an aphid

that undergoes a

holocyclic life cycle

outdoors – and alternates

hosts

Overwintering egg

laid near the bud

Stem mother, the stage

that hatches from the

overwintering egg

On the winter host plant the first generations may cause

leaf curling injuries to the new growth

Sometime, usually in June, the green peach aphids on the winter host

switch to becoming all winged forms – that then disperse to the

“summer hosts”

Summer hosts

include various

vegetables and

weeds

Spinach, lettuce, peppers,

potato, cabbage, pigweed,

and lambsquarters are

common summer hosts

Willow-Carrot AphidCaveriella aegopodii

Winter Host: Certain European willows

Summer Hosts: Various Carrot Family

(Apiaceae) plants (parsley, dill, carrot)

Lysimachia AphidThecabius lysimachiae

Winter Host: Black poplar (P. nigra)

Summer Host: Lysimachia (moneywort,

creeping jenny)

Cabbage AphidBrevicoryne brassicae

One of the very few aphids that

may survive Idaho winters

outdoors as actively developing

stages (nymphs, adults)

No eggs are produced no

males and mating occurs

– anholocyclic life cycle

Life History of Aphids• Holocyclic life cycle

– Involves one sexual generation (sexual form female and male)

– Results in externally laid egg to survive winter

– Often involves alternation of host plants• Winter host (Fall-late Spring)

• Summer host

• Anholocyclic life cycle– Continuous reproduction without sexual

reproduction or externally laid eggs

How Do Aphids Survive

Winter in Areas with

Freezing Temperatures?

• Outdoors

– Eggs that remain dormant through winter• Survives on perennial host or crop debris

– Nymphs, adults in continuous reproduction

• Rare and requires living hosts through winter

• Indoors

– Nymphs, adults in continuous reproduction

Primary aphid

species found in

greenhouses

Green peach aphid

Cotton-melon aphid Potato aphid

Indoors there is continuous,

asexual reproduction. There

are no eggs produced, nor

sexual forms (males, sexual form

females) [anholocyclic life cycle]

Plant Injuries Aphids May

Produce

• Contamination of produce

• Reduced vigor from heavy,

sustained feeding– Leaf yellowing, premature senescence

• Nuisance problems with honeydew

• Leafcurl distortions of new growth

• Vectors of some viral diseases

Piercing-sucking

mouthparts of

Hemiptera

In Hemiptera, the mandibles and maxillae become

extremely elongated to produce a stylet bundle.

The stylet bundle is sheltered within the labium to

produce a “beak” (proboscis).

Some sort of

“beak” is present

on the underside

of the head

Probocis containing

aphid mouthparts

Stylet bundle (mandibles and maxillae)

meandering through plant en route to phloem

Aphids use their mouthparts to

access the fluids of the phloem.

Little, if any, cell injury is

produced by most aphids.

Important Note:

Presence of aphids

does not always equate

to occurrence of plant

injury!

Sustained feeding by high

populations of aphids can

produce wilting, leaf yellowing,

retarded growth

Outdoors there are normally numerous natural enemies

usually control aphids before serious damage occurs

Flower fly larva

Green lacewing larva

Lady beetle larva

Honeydew

production

Uptake of phloem fluids here

Emergence of “honeydew” here

Leaf with sparkles of honeydew – and cast skins

The leaf above

the honeydew –

an aphid colony

Leaf with sparkles of honeydew – and cast skins

Honeydew Producing Insects*

• Aphids

• Soft scales

• Whiteflies

• Mealybugs

• Psyllids (some)

• Leafhoppers (phloem feeding

species)

*All suck sap from the phloem

Mealybugs

Soft Scales

WhitefliesPsyllids (some)

Sooty Molds

Fungi that grow on honeydew-contaminated

surfaces

Sooty mold

growing on

linden aphid

honeydew

Ants are commonly

associated with

honeydew producing

insects

Ants and Aphids

A Mutualistic Relationship

-Aphids provide

food – honeydew

-Ants provide

protection

Leafcurl Injuries

Produced by aphid feeding on emergent growth,

producing distortion

Leafcurl Plum

Aphid Injury

Hawthorn Chokecherry

Peach

Leafcurl Ash Aphid

Honeysuckle Witches’

Broom Aphid

Leaf curling produced by snowball (viburnum) aphid

Aphid Control - Scenario One

Aphids are Exposed

on the Plant

Different Levels of Control

Response to Aphids

• Do nothing. Natural controls will

ultimately take care of things.– Indoor production will require introduction

of natural enemies

• Treat the plants with a strong jet of

water to kill aphids

• Use a soap/detergent spray to kill

aphids

• Use some other effective ‘aphicide’

Check for aphid

natural enemies!

Photograph courtesy of David Cappaert

Diagnostic: Cast Skins Remain after Aphids Molt

Photographs courtesy of

Brian Valentine

Aphid

Parasitoids

Aphid

mummies

Parasitized aphids –

“aphid mummies”

Parasitoid wasp larva

inside aphid mummy

Parasitoid wasp emerging

from aphid mummy

Old aphid mummy with exit

hole made by emerging wasp

Lady beetle larvae

Pupae

Adults

Eggs

Lady Beetle Life Stages

There can be different levels of

response to an aphids infestation

• Do nothing. Natural controls will

ultimately take care of things.

• Treat the plants with a strong jet of

water to kill aphids

• Use an effective ‘aphicide’

– Contact sprays

– Systemic insecticides

Hosing for aphid control

Rose Aphids - Before

Rose Aphids - After

Some aphid control products –

Exposed Aphids

• Insecticidal Soaps

• Pyrethroids

–Bifenthrin, cyhalothrin,

cyfluthrin, etc.

• Neonicotinoids

–Imidacloprid

–Acetamiprid

Aphids have

already produced

a leaf curl?

Insects that work by

contact will not

control this problem –

and can easily make

it worse

Systemic insecticides

applied to leavesSystemic insecticides

applied to soil

For control of aphids in

existing leafcurls only an

insecticide that moves

systemically in plants will

provide control

Acetamiprid for

Aphid Control

• Best used as a spray

• Has systemic activity in plant

– May kill through ingestion or contact

• Extended residual activity

– May kill aphids for days-week?

– Fairly conservative of natural enemies

Insecticide control options for aphids

Commercial formulation for

ornamentals

Commercial formulation

for fruits and vegetables

Retail formulation

Acetamiprid formulations

Comparison of UV Stability among

Neonicotinoid Insecticides

0

5

10

15

20

25

30

35

Ha

lf l

ife (

da

ys)

Aquatic Photolysis

Acetamiprid

Imidacloprid

Thiamethoxam

Dinotefuran

Clothianidin

Data obtained from published EPA registration documents

Slide Credit: R. Fletcher

UV Stability

Neonictoinoids are generally not UV stable. Foliar persistence can be shortened by this feature.

Acetamiprid is

an exception.

Acute Toxicity of Neonicotinoids

to Adult Honey Bees

(Oral LD50 – micrograms/bee)

• Acetamiprid 14.53

• Imidacloprid 0.005

• Dinotefuran 0.056

• Thiamethoxam 0.005

• Chlothianidin 0.0003

Imidacloprid for

Aphid Control

• Best used as a soil application

• Has systemic activity in plant

• Slow uptake/Extended residual

activity

– May kill aphids for weeks- months?

– Conservative of some natural enemies

Insecticide control options for

aphids

Dormant Oils?

May manage many spring

aphid problems – if they

spend winter as eggs on

the plant

Aphid

egg

Oils can kill overwintering eggs of aphids. The

application must cover the egg, which can then

be killed by suffocation.

No overwintered egg

– no stem mother

No overwintering egg, no spring leaf curl

Spider MitesAcari: Tetranychidae

Photograph by Eric DayPhotograph by Ward Strong

Spider mites pierce cells with

their whip-like chelicerae

Typically they will destroy 1 to 2

dozen cells at each feeding site –

then move on

“Rototill and Suck”

Each feeding site produces a

small area of dead cells – a

type of stippling injury

With high mite populations,

the stippling injuries may

cover much of the leaf area.

Leaf bronzing A response seen in many plants in reaction to

spider mite damage

Symptoms on

evergreens are more

subtle – A duller, grayer

color is typical

In high populations, some spider mites will produce visible silk

Silk can protect the spider

mites and provide

pathways for movement

across a plant.

Life Stages of the Twospotted Spider Mite

Male spider

mite

Female spider mite with eggs Photographs courtesy of

David Shetlar

Spider mites lay eggs

that are quite large in

proportion to their body

Honeylocust spider mites, eggs and discarded skins

Mites can disperse by

wind-borne

‘ballooning’

Color change in mites going into dormancy (Diapause)

Green summer form

on leaves

Orange-red overwintering form

around buds

Seasonal color

changes in

honeylocust spider

mite

Honeylocust Spider

Mite

Platytetranychus gleditsiae

Conifer spider mites

Colorado species are

common on junipers,

arborvitae, and ponderosa

pine

Photograph by Bruce Watt

Photograph by Petr Kapitola

Photograph by

Petra Kapitola

Webbing on

needles

Adult and discarded skins

Eggs on twigs

and needles

Spruce

Spider Mite

Peak activity of mites - fall, spring

Peak expression of symptoms -

summer

Mites on conifers

are “cool-

season” species

Spider Mite Management

• Monitor high risk plants

• Minimize drought stress

• Maintain fairly high humidity

• Take particular care with

pesticide use on mite sensitive

plants

Sample plants to

detect potential

outbreaks

Spider mites always leave

behind cast skins and egg

shells – great for diagnostics!

Cast skins

Live spider mites, eggs and cast skins

Interactions of Drought, Drying and

Spider Mites on Landscape Plants

• Physiological effects acting through

host plant

–Changes in host suitability

–Changes in tolerance to mite injuries

• Alteration of leaf surface temperatures

• Interactions with relative humidity

• Physical effects of irrigation

Interactions of Drought and

Spider Mites

Drought-stressed plants may be more nutritionally suitable hosts.

Leaf surface temperatures increase on drought stressed plants

Interactions of Dry Air/Low Humidity

and Spider Mites

• Dry air allows spider mites to

more rapidly evaporate waste

fluid

• Dry air is often seriously

stressful to spider mite

predators

Natural enemies of spider mites

Minute pirate bug (feeding on thrips

Predatory mite feeding on spider mite

Predatory thrips

“Spider mite destroyer” lady beetles

Predatory Mite: Galendromus occidentalis

Optimal environmental conditions

80-100 degrees F> 50% RH

Predatory Mite: Mesoseiulus longipes

Can only tolerate the very low humidity of 40% when the temperature is 70°F.

Requires increasing humidity as temperature rises.

Drought stress greatly contributes to spider mite problems

Next to house, SW exposureAbout 6 feet from building,

on support trellis of porch

Another example.

Honeylocust spider

mites primarily are

pests on street trees

in Colorado.

A strong jet of water

can wash off many

spider mites from

plants

Mite Control Products

• Least disruptive of natural enemies– Floramite (bifenazate)

– TetraSan (extoxazole)

– Hexygon (hexythiazox)

– Horticultural oils

• Moderately disruptive of natural

enemies– Forbid (spiromesifan)

– Avid (abamectin)

• Highly destructive to natural enemies– All pyrethroids (Onyx, Talstar, Scimitar…)

Use of many

pesticides can

aggravate (‘flare’)

problems with

spider mites

Predators of spider mites

include minute pirate bugs (left),

predatory mites (below left) and

predatory thrips (below)

Mite Control Products

• Moderately disruptive of natural enemies

– Forbid (spiromesifan)

– Avid (abamectin)

• Highly destructive to natural enemies

– All pyrethroids (Onyx, Astro, Tempo, Scimitar…)

Least disruptive of natural enemies

Floramite (bifenazate)

TetraSan (extoxazole)

Hexygon (hexythiazox)

Horticultural oils

Horticultural Oils

Mite Control Products

• Least disruptive of natural enemies

– Floramite (bifenazate)

– TetraSan (extoxazole)

– Hexygon (hexythiazox)

– Horticultural oils

• Moderately disruptive of natural enemies

–Forbid (spiromesifan)

–Avid (abamectin)

• Highly destructive to natural enemies

–All pyrethroids (Onyx, Tempo, Astro,

Scimitar…)

Imidacloprid

and Spider

Mites

Observation, mid 1990s

– Spider mites seemed

to be a new problem on

many plants treated with

imidacloprid

Far more spider mites

and injury occurred

on plants treated with

imidacloprid

Why? Original thought was

that imidacloprid was killing

the natural enemies of spider

mites.

Some neonicotinoids

(imidacloprid,

chlothianidin) can

suppress the jasmonic

acid pathway – a

primary plant defense

mechanism

Spider Mite Management

• Monitor high risk plants

• Minimize drought stress

• Increase humidity

• Take particular care with pesticide

use on mite sensitive plants